The human polyomavirus, JCV, causes a demyelinating disease in immune compromised individuals, progressive multifocal leukoencephalopathy (PML). PML is a substantial neurological complication in AIDS patients, occuring in 8% of all cases. PML is the AIDS defining illness in almost 1% of AIDS cases. Although in the past PML was a rare disease, its incidence is high in immune compromised patients like AIDS and allograft recipients. JC Virus was orignially thought to be strictly neurotropic, infecting only macroglial cells derived from the human brain. However, our results have now shown that there is a firm link between susceptible lymphoid and glial cells in the pathogenesis of JCV infection leading to demyelination in the human brain. The data indicate that the same viral genotype which is found in brain tissue of PML patients originates from an initial lymphoid cell infection, including the bone marrow. The molecular similarities for JCV gene expression between cells of the nervous and immune systems directly correlated with the expression of the NF-1 class D family of DNA binding proteins which function for viral transcription. We have cloned the gene for NF-1/D from human brain which is highly expressed. There is a close association between susceptibility of infection to JCV and expression of this DNA binding protein. We have made expression vectors for all four class members of the NF-1 family. We have made a unique human brain derived, multipotential progentior cell line that can differentiate to either neurons or glial cells. We have been able to over express NF-1/D in human neurons differentiated from human CNS progenitor cells that are not susceptible to infection since these cells do not express competent levels of NF-1/D. The NF-1/D over expressing neurons however are susceptible to JCV infection, confirming the necessary regulatory function of this transcription factor as we have shown in the past in hematopoietic cells. We have also determined that JCV infection of human multiotential progenitor cells results in viral multiplication that is augmented 10 fold when differentiated to astrocytes but shut off when differentiated to neurons. New experiments have shown that infection can be reversed if the lineage is directed either back to progenitor cells or from glial cells to neurons. As a part of these studies, we have demonstrated that virus infection kills human glial cells as a lytic, necrotic cell death and not an apoptotic cell death as previously described by others. As a CLIA certified laboratory we have also participated in collaborative, viral diagnostic work that identified the human BK polyomavirus assoicated with allograft recipients published in the New England Journal of Medicine. We also have surveyed over 600 serum samples and determined that kidney donors with high antibody titers to BKV may pass on the infection to the recipient. We have also conducted a large scale review of patient CSF and plasma samples from over 400 MS patients and normal aged and gender matched controls to determine whether JCV DNA is present in PML patients. This has been part of an evaluation of the risk of MS patients treated with natalizumab, a humanized monoclonal antibody that prevents T cell migration into the brain. It is clear that JCV DNA can be found only in the CSF of PML patients further validating the PCR analysis of CSF as a diagnostic tool for PML.